An ongoing challenge in computer imaging technology is that of acceptably rendering digitized images on display devices which were incapable of reproducing the full spectrum of intensities or colors present in the source image. Continuous-tone images are commonly halftoned, i.e. rendered to a bitonal image for output by such devices.
Hiding information in continuous-tone image data, often referred to as watermarking, is an established practice in the field of information technology. However the nature of such encoded images can change considerably when halftoned for printing. There is a need for processes of encoding data in images in ways that survive the halftoning process.